Julen Molinuevo López

This work investigates the synergistic effect of femtosecond laser surface texturing (LST) and AlCrN coating on the wear performance of fine blanking tools. Dimple textures with 10, 15% and 20% surface coverage were fabricated on AISI M2 steel and coated with 1.5 µm AlCrN coating via HIPIMS. SEM and optical confocal microscopy confirmed the high geometrical accuracy of LST features and good coating adhesion at the coating-dimple interface. Contact angle measurements indicated that the as-coated surfaces were oleophilic, while increasing the textured area density led to a progressive shift toward higher contact angles, indicating a modification of lubricant spreading behavior. Ball-on-disk tests were performed under loads of 10, 30 and 50 N trying to simulate fine blanking contact conditions. An initial lubricant supply of 0.05 mL was sufficient to maintain a stable separation film, resulting in friction coefficients between 0.10 and 0.14 regardless of textured area density. In terms of wear, uncoated dimple-textured surfaces did not yield beneficial behaviour, showing higher wear rates than the untextured surface. In contrast, the application of the AlCrN coating on the untextured surface resulted in an approximately 90% reduction in the wear coefficient. A comparable wear reduction was observed for the sample textured at 10% dimple density; however, further increases in texture density led to an exponential increase in wear rate. SEM/EDX observations indicate that debris entrapment within the dimples promote third-body abrasion, contributing to the increased wear at higher texture densities.

Over the last decades, the study of surface functionalization regarding the concept of wettability has been on the rise. The number of papers published on the modification of a surface's natural ability to retain or repel a droplet has grown exponentially from the 1980s to the present day. Through purely superficial changes in inherent material properties such as wettability, laser surface texturing has emerged as one of the most interesting technologies for applications related to the generation of superhydrophobic surfaces that promote easy cleaning or reduce the adhesion of water in liquid and/or solid state. However, the process of achieving surfaces with specific wettability properties, i.e. with a desired minimum contact angle, can consist of a large number of trial-and-error steps including: i. Parametrization of the laser micromachining process ii. Characterization of the introduced surface modification: topography and morphology iii. Functional characterization of the surface. This process must be repeated for each manufactured texture, which leads to an increase in manufacturing time, with its associated economic cost. For this reason, wettability prediction models for surfaces undergoing both physical and chemical modifications have been proposed over the last decades to reduce this cost. In this thesis, the main objective is to provide a guide for future materials and feature geometries, showing the steps to follow to study the effect of different topographical parameters that define a texture on the contact angle, as well as introducing a simulation modelling tool to predict which type of texture and/or dimensions offer the best results. This is intended to reduce the window of dimensions to be considered and, consequently, to reduce the experimentation time. Thus, the process of selecting textures to achieve specific wettability objectives would be streamlined not only at the laboratory level but also at more relevant environments (at a more industrial levels), which could lead to throughput improvements in terms of surface functionalization. In order to achieve the objective described above, this thesis proposes the elaboration of a Design of Experiments in which a number of textures are fabricated by means of ultrashort pulse laser technology in a polymeric material with a relatively high use in the industry such as polypropylene. Beforehand, a complete study is performed regarding the comparison between two pulse emission modes (Single Pulse and Pulse Train or Burst Mode). The main advantages and disadvantages of both operation modes have been evaluated and those parameters that allow an optimal quality/throughput ratio for the considered application have been identified. Once selected the optimal parameters, the corresponding textures have been developed. The Design of Experiments focuses on the evaluation of the probabilities of each factor in the modification of the contact angle, and a simplified prediction model obtained by regression is proposed. The experimental results for the Design of Experiments serve as validation parameters for the simulation of wettability at different textures, performed with COMSOL Multiphysics. A finite element model is proposed with the CFD (Computer Fluidic Dynamics) module, which makes use of the union of two physics such as the kinetics of the fluid (Laminar Flow) and the identification of two different phases in a medium, divided by an interface (Two Phase Flow, Phase Field). In this case, the effect of different simulation parameters on the results is studied and the optimal mesh size is established to provide results (in terms of contact angle) similar to the experimental ones. The results allow understanding the effect of each topographical factor defining a texture on the final surface wettability and provide a map of results similar to those observed experimentally. RESUMEN Durante las últimas décadas, el estudio de la funcionalización de superficies en lo que respecta al concepto de mojabilidad ha ido in crescendo. El número de artículos publicados en relación a la modificación de la capacidad natural de una superficie a retener o repeler una gota ha crecido de forma exponencial desde los años 80 hasta hoy en día. A través de cambios exclusivamente superficiales de propiedades inherentes del material como es la mojabilidad, se ha demostrado que el texturizado por láser de una superficie es una de las tecnologías con mayor interés en aplicaciones relacionadas con la generación de superficies superhidrófobas que fomentan la fácil limpieza o que logran reducir la adherencia del agua en estado líquido y/o sólido. Sin embargo, el proceso para lograr superficies con propiedades de mojabilidad específicas, es decir, con un ángulo de contacto mínimo deseado, puede consistir en un gran número de pasos de prueba y error que incluyen: i. Parametrización del proceso de micro fabricación por láser ii. Caracterización de la modificación superficial introducida: topografía y morfología iii. Caracterización funcional de la superficie. Este proceso se tiene que repetir para cada textura fabricada, lo cual conlleva un aumento del tiempo de fabricación, con su coste económico asociado. Por esta razón, durante las últimas décadas se han propuesto modelos de predicción de mojabilidad en superficies sometidas a modificaciones tanto físicas como químicas para reducir este costo. En esta tesis, el objetivo principal es proporcionar una guía para futuros materiales y geometrías, en la que se muestre los pasos a seguir para estudiar el efecto de diferentes parámetros que definen una textura en el ángulo de contacto, además de introducir una herramienta de modelado por simulación para predecir qué tipo de textura y/o...